A Private Business Exchange (PBX) is a private switching element that provides its business users with features and access to the public network. Calls that are made to a PBX station from the Public Switched Telephone Network (PSTN) are routed to a Class 5 switch serving that PBX. The Class 5 switch routes the calls over PBX trunks to the PBX for termination to the stations served by the PBX. When a PBX user originates a call to the PSTN, the user typically dials an access digit, i.e., "9", plus the called party's telephone number. The call is then forwarded to the serving Class 5 switch in the PSTN for termination to the called party. The calls among stations served by the PBX are processed internally to the PBX. The PBX is also responsible for providing features, such as abbreviated dialing, call forwarding, call transfer, etc., to the PBX stations. A Centrex arrangement provides similar functions except the stations in the business environment are served directly from the Class 5 switch which includes specific software to provide business features similar to those features provided by the PBX. In this arrangement, a switch may not be located on the business customer's premises.
In both the PBX and the Centrex environments, equipment is available to the business customer which allows them to provide wireless access to their users. A known prior art system is illustrated in FIG. 1. A Class 5 switch 10, such as a Service Switching Point (SSP), serves a PBX 12 via a plurality of PBX trunks 14. The PBX 12 allows users to use a desktop telephone 16 as well as a wireless handset 18. Wireless service is provided to the wireless handset 18 via an adjunct 20 that provides radio port control functionality to manage micro cells (radio base stations) 22 that are located strategically in the business environment to provide in-building coverage for the PBX users. This adjunct 20 enables the users to have mobility within a specific radio coverage environment, such as a building or a campus. However, if the user moves too far from the business environment, they may move outside the coverage area of the micro cells 22 and not be able to use their wireless handset 18.
A public wireless radio network, or Personal Communication Service (PCS), typically includes a PCS switch 24 in communication with a Base Station Controller (BSC) 26. BSC 26 controls a plurality of Base Stations (BSS) 28 which provide cellular service to various wireless handsets 30 (only one is shown). Currently, however, there is no mechanism for allowing the user of the wireless handset 18 in the PBX system to roam into the PCS system and take advantage of the wireless coverage provided by BSC 26 while still allowing the PBX/Centrex system to maintain control of the user's features and call processing.
A lack of interworking capability between wireless business systems and public wireless networks introduces several drawbacks. The primary drawbacks include no hand-off of a call between the public and private networks and the inability for a wireless PBX user to be able to receive a call while roaming in a public wireless network.
An integrated PCS network is disclosed in U.S. Pat. No. 5,506,887 issued to Emery et al. Emery discloses a system structure for interfacing the capabilities of a land line telephone system with a radio link communications system and controls the provision of private network service features to users of both radio link systems and land line systems. Call processing data associated with each subscriber is stored in a central service control point, or database, within the network. Call routing can then be provided to either a land line or a wireless unit via a mobility controller in communication with the database in response to calls directed to the user's single telephone number. Thus, the system disclosed by Emery provides all the services unique to both the land line telephone system and the radio system to the user via one single telephone number and a central database. Emery, however, fails to disclose a system architecture that integrates an existing PBX wireless network and an existing PCS network so that a subscriber of the PBX wireless network can roam into the public PCS network without any action being taken by the subscriber.
Thus, there exists a need to provide a flexible network architecture that integrates the features and services provided by a private business network with the unlimited roaming capability associated with the public wireless network.